The invention relates to video image processing, and in particular to a method and device for determining the spacing between video signal values.
First and second sequences of video signals are obtained, for example, in video image processing, when the image information, in the form of pixels, of two temporally sequential fields with offset raster positions and built up line-by-line are read column-by-column. The first sequence of video signals relates to the image information in the first field, while the second sequence of video signals relates to the image information in the second field. Fields of this type include, for example, interlaced television pictures at a frequency of 50 Hz/60 Hz. Determination of the spacing between the two signal sequences is necessary, for example, to determine whether, or by what degree, two successive images or image segments of an image sequence differ. This information is required, for example, to determine whether the image sequence is displaying a still image or a moving image sequence. Depending on the result, it is then possible, for example, to select the appropriate algorithms (e.g., interpolation algorithms) to generate intermediate images.
Due to the difference in raster positions, the two interlaced fields cannot be compared pixel for pixel, nor can the two signal sequences be compared signal value by signal value. The inherent problem with interlaced fields is that for the pixel positions to which image information values are assigned in the first field, there are no corresponding pixels and thus no image information values in the second field. The two interlaced fields are complementary.
In response, for each of the two successive signal values of a first signal sequence obtained through column-by-column reading of a first field, a signal value is assigned from a second signal sequence obtained through column-by-column reading of a second field. The signal value of the second sequence is temporally or spatially assigned to the two signal values of the first signal sequence by the fact that this value is associated with a pixel position that is located between the pixel positions of the associated two signal values of the first sequence.
A known approach to comparing images/image segments of the type having different raster positions is to first perform a pixel interpolation procedure that assigns to each pixel of the first field a corresponding pixel in the second field. A comparison procedure can be implemented after each pixel of a first image has been assigned a pixel at the corresponding position in the second image. The two images are compared pixel by pixel, and the quantities of the differences for the image information values assigned to the individual pixels are added up.
The quality of the spacing determination depends to a significant degree on the quality of the interpolation procedure, and interpolation procedures which perform a reliable pixel interpolation are complex in their implementation.
Other signal sequences in which one signal value of a second signal sequence is assigned to two signal values within a first signal sequence include, for example, measurement series generated by regular measurement of a physical parameter. Therein, the measurement times of the two series are temporally offset with the result that a measured value of the first series is always recorded temporally between two measured values of the second series, and vice versa. For these signal sequences as well, it is desirable to determine their spacing without the necessity of previously generating interpolated intermediate values for the two series using a complex interpolation procedure.
What is needed is an effective method and device for determining the spacing between two signal sequences that define images having different raster positions, and which does not require a complex interpolation procedure.